The present invention relates to bridge structures, such as air bridges, used in the fabrication of semiconductor devices. More particularly, the present invention relates to bridge structures formed of aluminum based alloys and methods of forming such bridge structures.
Dimensions in integrated surfaces are constantly being reduced. For example, the separation between conductive layers in material is being reduced in order to achieve smaller integrated circuits. By reducing the spacing of conductive materials in an integrated circuit, an increase in capacitive crosstalk is observed. Conventional integrated circuits typically utilize interconnect structures wherein a first metal line is separated from a second metal line by an insulative material. If the capacitive effects between the first metal line and the second metal line is high, i.e., a voltage on one effects a voltage on the other, then the capacitive effects may lead to an inoperable integrated circuit. Even when the capacitive coupling is insufficient to cause cross-talk, making the system inoperable, the increased resistance-capacitance (RC) effect will reduce the maximum operating speed of the circuit.
In order to reduce such capacitive coupling, low dielectric constant materials have been utilized between such conductive materials or lines. However, use of low dielectric constant materials have many associated problems. For example, equipment is not always available to properly process new low dielectric materials in various integrated circuits. Further, for example, such dielectric materials may not properly or adequately reduce such capacitive coupling between the conductive materials.
Bridge structures, such as air bridges, have provided integrated circuit designers with a method to reduce such capacitive coupling. The air bridge will become a commonly used low capacitive wiring structure as dimensions become smaller and wiring capacitive/resistive effects between conductive materials in integrated circuits become a larger portion of the delay associated with operation of a semiconductor device. For example, an air bridge provides a simple technique for crossing over a conductor when forming an interconnect between two other conductive material regions of an integrated circuit.
However, an air bridge cannot be made indefinitely long. The maximum length of an air bridge, e.g., the length from one pillar or support structure of the overall air bridge structure to the next support structure, is determined by either how long the air bridge can be before it breaks or is determined by how long the air bridge can be before it sags under the air bridge""s own weight such that it contacts another portion of the device structure or circuit being fabricated leading to short circuit or other operational problems. The presently utilized metals or alloys for forming air bridges, such as, for example, gold, aluminum, aluminum/copper alloy, aluminum/copper/silicon alloy, and tungsten, do not provide for air bridges of adequate length in many circumstances.
For the above reasons, there is a need in the art for bridge structures, such as air bridges, formed of new metals or alloys. In addition, there is a need for methods of forming such bridge strictures using such metals or alloys to provide bridge structures of effective lengths. The present invention, as described below, overcomes the problems described above, and other problems which will become apparent to one skilled in the art from the detailed description below.
The present invention includes a bridge structure. The bridge structure includes a bridge element formed of an alloy comprising aluminum, copper, and lithium.
In other embodiments of the bridge structure, the alloy may further include silicon and the alloy may include an amount of lithium greater than about 1.0 percent by weight up to the maximum solubility limit of lithium in aluminum.
Another bridge structure in accordance with the present invention includes a bridge element formed of an alloy including aluminum, about 1.0 to about 4.2 percent by weight of lithium, about 0.2 to about 5 percent by weight of copper, and 0 to about 1.6 percent by weight of silicon.
A method of forming a bridge structure in accordance with the present invention is also described. The method includes providing a surface and forming a removable region of material over a portion of the surface. A bridge element is formed over the removable region of material. The bridge element is formed of an alloy including aluminum, copper, and lithium. The removable region of material is removed.
The present invention also includes an air bridge. The air bridge includes abridge element formed of an alloy comprising aluminum, copper, and lithium.
In one embodiment of the air bridge, the alloy further includes silicon. In another embodiment, the alloy includes an amount of lithium greater than about 1% by weight up to the maximum solubility limit of lithium in aluminum.
Another air bridge in accordance with the present invention includes a bridge element. The bridge element is formed of an alloy comprising aluminum, about 1 to about 4.2% by weight of lithium, about 0.2 to about 5.0% by weight of copper, and 0 to about 1.6% by weight of silicon.
Another air bridge in accordance with the present invention for use as an interconnect is described. The air bridge includes a bridge element formed of an alloy consisting essentially of aluminum, copper, and lithium. In one embodiment of the air bridge, the alloy includes an amount of lithium greater than about 1.0% by weight up to the maximum solubility limit of lithium in aluminum.
Yet another air bridge in accordance with the present invention for use as an interconnect is described. This air bridge includes a bridge element formed of an alloy consisting essentially of aluminum, copper, lithium, and silicon. In one embodiment of this air bridge, the alloy includes an amount of lithium greater than about 1.0% by weight up to the maximum solubility limit of lithium in aluminum. In another embodiment of this air bridge, the alloy includes silicon in an amount of about 1.0% or more up to the maximum amount of solubility limit of silicon in aluminum.
A method of forming an air bridge in accordance with the present invention is also described. The method includes providing a surface and forming a removable region of material over a portion of the surface. A bridge element is formed over the removable region of material. The bridge element is formed of an alloy comprising aluminum, copper, and lithium. The removable region of material is removed to define an air gap between the surface and the bridge element. In one embodiment of this method, the alloy further includes silicon.
Another method of forming an air bridge interconnect is also described. The method includes providing a substrate assembly having two contact regions. Each of the contact regions have a diffusion barrier associated therewith. A removable region of material is formed over a portion of the substrate assembly between the two contact regions. A bridge element is formed over the removable region of material and in contact with each of the contact regions. The bridge element is formed of an alloy consisting essentially of aluminum, copper, and lithium. The removable region of material is removed to define an air gap between the substrate assembly and the bridge element.